In recent years, piezoelectric devices such as piezoelectric resonators, piezoelectric oscillators are widely used in hard disk drives (HDD), mobile computers, information apparatuses such as IC cards and portable communication apparatuses such as cellular phones, phones for automobiles, and mobile communication devices such as pacing systems.
Piezoelectric devices are structured such that a piezoelectric resonator element as an electronic part is contained in a package, to which a lid as a cover body is hermetically bonded.
In piezoelectric devices, the ambient environment of the piezoelectric resonator element changes due to bonding of the lid. Therefore, there arises great necessity to accurately adjust the frequency of the piezoelectric resonator elements after sealing.
However, the lid is usually made from metal. Thus, after the package has been sealed, it is impossible to perform the frequency of the lid by performing treatment to the piezoelectric resonator element arranged therein.
In view of the above, such a piezoelectric device as shown in FIG. 10 is also proposed (refer to, for example, JP 2005-130093).
As shown in FIG. 10, the piezoelectric device 11 contains the piezoelectric resonator element 6 as an electronic part in the package 2.
An electrode portion 3 is formed in the package 2 and is electrically conducted to mounting terminals 5, 5 in the package, the mounting terminals being disposed outside of the package. Conductive adhesive 4 is applied on the top of the electrode portion 3. The lid 7 is hermetically sealed with a bottom portion of the piezoelectric resonator element 6 being laid and fixed on the top of the electrode portion 3, on which conductive adhesive 4 has been applied.
The lid 7 has an aperture, thorough which glass is mounted to thereby form a window 8.
As thus described above, even after the lid has been sealed, it is possible to perform frequency adjustment using mass reduction technique by irradiating a part of an electrode of the piezoelectric resonator element 6 with laser light LB from outside through the window 8.
However, in the case of the piezoelectric device 1 shown in FIG. 10, step for forming the window 8 by forming an aperture in a part of the lid 7 and mounting the glass through the aperture. Therefore, the process becomes complicated, which involves increase in manufacturing cost. Such step is hardly performed especially when the product itself is downsized.
Further, there is also a way to make the lid itself from glass.
In this case, when the plate member made from glass constituting the lid is bonded to the member such as a package made from ceramic, low-melting glass having melting point of 320 degrees Celsius (hereinafter, all of the temperature indications described below are based on the temperature scale of Celsius) is used as bonding material.
However, such type of low-melting glass contains lead. The use of sealing materials containing lead may lead to environmental contamination and is therefore undesirable.
Thus, low-melting glass containing no lead is used. However, such low-melting glass has melting point of more than 400 degrees, which is relatively high. Therefore, there arises a fear in that the properties of the piezoelectric resonator element itself may be deteriorated. Further, researches is made on low-melting glass having relatively low melting point, which is, however, very expensive.
In view of the above, metal film is formed on the lid made from glass and sealing materials (brazing materials) made from metal is used. As brazing materials made from metal, solder is known. In particular, solder containing no lead, that is to say, lead-free solder, is alloy made from tin, silver, copper etc. and has low temperature of about 200 to 220 degrees. Thus, there arises a fear in that lead-free solder may not withstand the reflow process when the piezoelectric device is mounted. Furthermore, when gas is generated after sealing and gas component is adhered to the piezoelectric resonator element, the Cl value is increased.